The invention relates generally to methods and apparatuses for hemodialysis and hemofiltration.
In recent years, porous membranes, either in hollow fiber or flat sheet configurations have found use in hemodialysis and hemofiltration. Hemodialysis membranes are porous membranes permitting the passage of low molecular weight solutes, typically less than 5,000 Daltons, such as urea, creatinine, uric acid, electrolytes and water, yet preventing the passage of higher molecular weight proteins and blood cellular elements. Hemofiltration, which more closely represents the filtration in the glomerulus of the kidney, requires even more permeable membranes allowing complete passage of solutes of molecular weight of less than 50,000 Daltons, and, in some cases, less than 20,000 Daltons. The polymers used in these membranes must possess excellent mechanical properties so as to support the fragile porous membrane structure during manufacture and use. In addition, the polymer must have adequate thermal properties so as not to degrade during high temperature steam sterilization processes. Furthermore these membranes must have excellent biocompatibility, such that protein fouling is minimized and thrombosis of the treated blood does not occur. Though polysulfones have the mechanical and thermal properties necessary for these applications, they are insufficiently hydrophilic. To improve their hydrophilicity, polysulfones have been blended with hydrophilic polymers such as polyvinylpyrollidinone (PVP). However, since PVP is water soluble it is slowly leached from the porous polymer matrix creating product variability. Notwithstanding, the method of blending polysulfone with a hydrophilic polymer such as PVP is a commercially used process for producing hydrophilic porous polysulfone membranes for hemofiltration and hemodialysis.
Thus porous membranes possessing excellent thermal and mechanical properties and excellent biocompatibility for hemodialysis and hemofiltration are desired. In addition, polymers capable of being fabricated into porous membranes that possess sufficient hydrophilicity to obviate the need for blending with a hydrophilic polymers is also desired. Finally polymers which are more hydrophilic than polysulfone yet not water soluble, which may induce hydrophilicity to the porous polysulfone membranes without undesirably leaching from the membrane are also sought.